Frost stat heating radiators

[wokerati]

Hi all,
Sorry if this is obvious, but as a plumbing novice and having spent a morning reading about how frost stat/pipe stats work I can't seem to find a definitive answer, so I thought I'd turn to this hivemind.
I have an open vented system with a Worcester boiler located in the garage, and a Honeywell thermostat inside. This morning I've also learned that I have a Honeywell frost stat above the boiler. ~
Because I'm rather financially tight I've been operating the thermostat on 'manual' - just flicking the CH on in the morning for a little bit; and only turning on HW when required.
Since the weather turned colder my boiler is kicking in with its frost protection mode - great! I can see a little snowflake sign on the indoor thermostat and hear the boiler chuntering away... but I've also noticed that when this is happening my radiators are heating up too. It's not staying on for hours and hours, but I'd rather not pay to heat the house if I'm not in/when I'm asleep.
My understanding is that the frost stat being located in the garage means it will turn on the boiler when the temp is around <5deg in the garage, and that there is probably a pipe stat somewhere that turns it back off again when the water in the return pipe is warm enough to avoid freezing.
What I can't understand is whether it should also be heating the radiators when it's on for frost protection? Would I theoretically save money by turning the radiators down/off when it's doing this? Or is it just heating the water to protect the system, which may as well be put into the radiators?
Thanks very much for any wisdom you can provide.

 

[RandomGrinch]

What indoor stat do you have?

 

[wokerati]

Honeywell Smartfit T8677A or T8617A (sorry, I can't tell the difference online and the manual is for both)

 

[RandomGrinch]

Honeywell Smartfit T8677A or T8617A (sorry, I can't tell the difference online and the manual

Thanks for that.
I may be wrong, and I’m not sure if your system matches the attached manual, but I was wondering if the snowflake symbol was related to the minimum room temperature setpoint, rather than the frost stat firing the boiler itself?

 

[ChrisJP]

I think the idea of the frost stat is to protect the whole system, both in the garage and in the house so that, if you are away from the house for a period in cold weather, nothing freezes up. So, the boiler running the radiators is as it's meant to be.
If you don't want this to happen, and you're confident that nothing in the house will freeze up, then you could laboriously turn off all the radiators before going out or going to bed, and then laboriously turn them back on again when you want heat in the house.
The other possible option would be to fit thermostatic valves with a frost setting on every radiator - these would stay closed until it got as cold in the house as it is in the garage when you boiler kicks in with its frost stat.

 

[Harry Bloomfield]

What I can't understand is whether it should also be heating the radiators when it's on for frost protection? Would I theoretically save money by turning the radiators down/off when it's doing this? Or is it just heating the water to protect the system, which may as well be put into the radiators?

There is no way, for the boiler system, to heat water, without circulating through the radiators. If, in fact it is your pipe stat, which is triggering the heating to come on, rather than the boilers own stat.[1] - then I would look at insulating the pipwork in your garage, as well as considering some form of electric trace heating, which incorporates it's own stat..

[1] The boiler's own stat., senses the temperature of the boiler core. They tend to be triggered more, if the flue faces the prevailing wind direction.

 

[wokerati]

Thanks all very much for such quick and helpful responses!

Harry Bloomfield & Chris JP, I think that you've answered my question in as much as it's not something to worry about and things are functioning more or less as designed. Like I said, as it's not coming on ridiculously often or when it's too hot indoors I'm happy just to leave it as it is. I suppose installing further clever electrics is likely to be a lot more expensive than just letting it keep the house slightly warmer than I require (I tend to keep it at a stingy 16-17deg)!

I may be wrong, and I’m not sure if your system matches the attached manual, but I was wondering if the snowflake symbol was related to the minimum room temperature setpoint, rather than the frost stat firing the boiler itself?

Thanks very much for looking into it. I had wondered the same thing myself, but there doesn't seem to be consistency re: the inside temperatures that are triggering it firing - I have a separate room thermometer which is ~16deg when the snowflake symbol is coming on. Weirdly the snowflake symbol isn't mentioned at all in my Honeywell manual!

 

[oilhead]

The manufacturers recommendation is for the pipe frost stat to be set at 25c ish. This means that the indoor circuit will be above this before the return reaches in the target temperature in the garage. In the past, where customers have baulked at the 'waste' of fuel, I have moved the pipe stat to the flow at the furthest point from the boiler at the exit to the house. As the flow and return pipes are invariably adjacent, and also the radiated heat from the boiler will temper the return, you get protection without excessive running.

 

[Harry Bloomfield]

I suppose installing further clever electrics is likely to be a lot more expensive than just letting it keep the house slightly warmer than I require (I tend to keep it at a stingy 16-17deg)!

Not necessarily - it depends on the amount of exposed pipework, and how well you insulate them. The trace heating, with built-in temperature sensing, will only consume power when near zero. It's an easy DIY install, cheap, just needs a socket to plug into.